The present invention relates generally to extrusion of an adhesive onto the underside of an object and more specifically, to the extrusion of isocyanate resin onto the bottom of a board in a Glulam operation.
In the manufacture of structural lumber, individual boards or veneers may be joined together in layers with adhesive bonding between layers. The resulting lumber and the process itself are often referred to as xe2x80x9cGlulam.xe2x80x9d
Typically, the Glulam process comprises conveying a board 11 on a conveyor 12 in direction xe2x80x9cAxe2x80x9d through a pair of adhesive-dampened rollers 14, 14xe2x80x2. The adhesive transfers from rollers 14, 14xe2x80x2 to the upper 16 and lower 18 surfaces of board 11 respectively, and the board is stacked on top of one or more other boards 11xe2x80x2 having a similar coating of adhesive thereon. Bottom roller 14xe2x80x2 may be kept freshly coated with adhesive by continually turning through a first reservoir 22, and top roller 14 may receive a constant drip or spray of adhesive from a second reservoir 20. When a sufficient number of board layers have been stacked, the stack is pressed together while the adhesive cures.
Such a process using rollers to apply the adhesive is adequate for use with adhesives such as polyvinylacetates (PVAs), phenol-formaldehydes, and urea formaldehydes that have been historically used in such operations. Isocyanates-based adhesives, however, which have certain process advantages over other binders such as faster cycle times, the ability to use higher moisture content components, and a lack of formaldehyde emissions, cannot be used with rollers. Because isocyanates react with moisture in the ambient air, the binder hardens on the rollers, rendering them useless for applying a uniform coating.
Isocyanates can, however, be extruded directly onto a board surface, because in an extrusion process, the adhesive stays within piping or tubing until it is discharged from the extrusion nozzle. This prevents adhesive contact with moisture until the adhesive hits the board surface, where reaction with moisture is desired.
Referring now to FIG. 2 there is shown a typical extrusion nozzle 110, known in the art for extrusion of an adhesive from above a board 11 on top of the board as it is conveyed in the direction of arrow xe2x80x9cBxe2x80x9d. Extrusion nozzle 110 comprises a body 200 that may simply be a pipe, capped on both ends with caps 210, and having a plurality of holes (not shown) penetrating through the pipe wall.
The appropriate adhesive is pumped into nozzle 110 through a pipeline or hose 215, and exits the nozzle through the holes in streams 220 that fall by gravity onto board 11. The plurality of holes and adhesive streams 220 therefrom create a series of evenly spaced lines on the board. The evenly-spaced lines assure a precise amount of glue is applied to provide the adequate coverage necessary to generate the bonding strength needed to conform to certain industry standards.
While such extrusion nozzles are well-known for extruding a substance onto the topside of an object, no adequate apparatus for extrusion of an adhesive onto the bottom surface of a board is known. Merely inverting nozzle 110 is inadequate, as gravity no longer works to the advantage of adhesive streams 220 exiting the nozzle holes, but instead works to pull the adhesive away from the board. So, although a standard extrusion nozzle could adequately substitute for roller 14 in a Glulam operation of FIG. 1, no apparatus to substitute for roller 14xe2x80x2 has been available, thus limiting the use of isocyanates in Glulam operations.
The present invention proposes an apparatus that enables extrusion of adhesive onto the underside of an object, such as a board in a Glulam operation, from underneath the object.
In accordance with this invention, there is provided an extrusion apparatus comprising an underside extrusion nozzle adapted to extrude a substance onto an object from underneath the object, the underside extrusion nozzle comprising: a body having an exterior surface and a manifold therein; at least one extrusion passage in the exterior surface, and preferably a plurality of extrusion passages, with each passage connecting to the manifold; and a scraper blade attached to the body exterior surface adjacent to the passages and defining a reservoir between the exterior surface and the scraper blade.
The extrusion apparatus may further comprise a stand for holding an underside extrusion nozzle having a cylindrical body, and a conveyor adapted to convey the object on top of the extrusion nozzle tangentially to the body circumference and perpendicular to the scraper blade.
The stand may further comprise at each of a first end and a second end of the underside extrusion nozzle body: a mounting bracket attached to the end; a supporting leg containing therein a spring attached to the mounting bracket, the spring adapted to bias the underside extrusion nozzle in contact with the object on the conveyor.
The invention may also comprise a process for joining a first object having a topside and an underside, to a second object having a topside and an underside, the process comprising the steps:
a) conveying the first object in a first direction;
b) extruding adhesive from a fixed location beneath the first object onto the first object underside as the first object is conveyed past the location; and
c) joining the first object underside together to the second object topside.
The process step (b) may further comprise extruding adhesive onto the first object topside from above the object simultaneously with extruding adhesive onto the first object underside from beneath the object.
The extrusion apparatus and process of this invention may be used with an adhesive based on an isocyanate resin.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, but are not restrictive, of the invention.